FM Limiter as AM Demodulator

[Synchrodyne]

There seems to be far more diversity of valves used in US FM sets than in the UK.

Yes.  I imagine that the very large US market supported a bigger diversity of valve developments than was the case elsewhere.  And new radio valves, not just new TV valves were developed right up to the end of the valve era.  For example, one 1960 American radio valve development was the introduction of a range of 100 mA series-string valves for use in compact AA5-style AM-only receivers, with less heat output than the established 150 mA type.

In the FM case, one might say that in Europe, the ECC85 was a plateau upon which the industry mostly parked itself until transistors took over.  On the other, in the USA, after a belated arrival, it was the starting point for significant development along several vectors.

Cheers,

Steve